The present invention relates to disc brakes for vehicles, and in particular to an arrangement for enhanced cooling of a brake disc.
Disc brakes are increasing being used on commercial vehicles, replacing conventional drum brakes. Very high braking energy is generated when the disc brake's caliper applies the brake pads to the brake disc to slow such heavy vehicles. In order to deal with such loads, very robust and often complicated designs have been required to connect the brake disc of a disc brake to transfer the braking forces from the brake disc to the axle hub on which the brake disc is mounted. The design of the brake disc-to-hub connection is further complicated by the need to ensure adequate flow of cooling air from the hub region into the interior ventilation channels of an internally ventilated brake disc.
Commercial vehicle brake discs, also referred to as “brake rotors” or “rotors,” often are mounted onto axle hubs using so-called spline arrangements using a fixed or floating connection, such as taught in U.S. Pat. Nos. 6,626,273 and 7,410,036. One example a semi-floating connection is the Splined Disc® brake assembly from Bendix Spicer Foundation Brake LLC. These types of brakes typically are mounted on an axle hub having a plurality of axially-oriented splines arranged around an outer circumference of a disc-mounting region of the hub. The brake disc has corresponding radially-inward facing tabs about the inner circumference of the brake disc. The disc is mounted to the axle hub by axially sliding the brake disc onto the hub's mating splines, followed by insertion and/or attachment of a variety of fasteners, brackets, etc., as necessary per the particular splined disc's design in order to secure the brake disc against axial movement off of the hub.
An alternative brake disc-to-hub connection arrangement is disclosed in co-pending application Ser. No. 14/640,152. In this approach, a brake disc is provided with a plurality of wedge-shaped slots about an inner circumference of the brake disc radially positioned in locations corresponding to brake disc mounting studs provided on an axle hub. The brake disc and the hub are connected to one another by wedge-shaped elements (aka “keys”) that are positioned in corresponding transverse wedge-shaped holes in a radially inner region of the brake disc, preferably with a retaining device that retains the keys in their respective holes in the brake disc.
A common issue with many approaches to connecting a brake disc to an axle hub is the blockage of cooling air from the inner radial region of the brake disc toward the outer radial region, where the cooling air is drawn through interior channels located in the brake disc between parallel friction rings by differential pressure between the relatively stagnant air near the hub and the relatively low pressure at the outer circumference of the brake disc created by the Bernoulli effect at the outer circumference.
With or without significant cooling air flow blockage by axle hub-to-brake disc mounting arrangements, many internally-ventilated brake disc cooling channel and vane arrangements are known in the art. These include, for example, vanes that extend radially outward from the inner radius of the brake disc friction surfaces, vanes that extend in straight lines that are offset at an angle relative to radially-oriented vanes, vanes having a curved shape, and vanes having different lengths (e.g., vanes with alternating starting distances from the inner radius of the friction rings).
The present invention provides an improved approach to internally-ventilated brake disc cooling channel and vane arrangements which enhances cooling air flow, despite the presence of substantial hub-to-brake disc connecting structures.
In an embodiment of the present invention, the internally ventilated brake disc is provided with at least one circumferential row of flow-modifying features radially outboard of, and adjacent to, the brake disc's hub-mounting structure. These flow-modifying features further are radially separated from the primary internal cooling vanes and channels of the brake disc.
The inventor has determined that the inclusion of such a radially-inner row of flow-modifying features to be highly effective at re-directing cooling air flow into adjacent cooling channels. These features effectively increase the pressure of the cooling air entering the cooling channels as compared to the pressure at the radially inner ends of the channels of a brake disc without the flow-modifying features, which would otherwise see a Bernoulli-induced pressure decrease at the radially inner ends of the channels (a lesser pressure decrease than at the higher velocity radially outer ends of the channels).
As the brake disc rotates, cooling air flow entering the radially inner region of the brake disc first passes radially outward through the hub-to-brake disc mounting elements. Emerging from the mounting element region, the cooling air encounters at least a first circumferential row of flow-modifying features, for example, round or oval cross-section bars between the two parallel friction rings. Because these flow-modifying features are rotating about the hub rotation axis at a higher angular velocity than the incoming cooling air, the flow-modifying features change the direction, velocity and relative pressure of the cooling air. By sizing an locating the flow-modifying features to suit the particular application, these features may be arranged such that the deflected cooling air is directed toward a particular vane or into a particular cooling channel, thereby increasing the cooling air mass flow in the channel to increase the amount of heat transfer and removal from the brake disc.
The present invention is not limited to a particular vane structure such as only straight cooling vanes and channels or only curved cooling vanes or channels. Rather, the present invention is directed to the inclusion of flow-modifying features immediately radially outside a brake disc's hub connection region that are tailored to re-direct the incoming cooling air flow in a more focused manner into the cooling channels. Further, the present invention is not limited to re-directing cooling air flow in a solely-radially outward direction, but instead uses the difference in angular velocity of a flow-modifying feature and the incoming cooling air flow to re-direct the cooling air flow into one or more cooling channels that are circumferentially displaced behind the flow-modifying feature.
The present invention is also not limited to flow-modifying features radially aligned with adjacent cooling channel vanes, but may include flow-modifying features that are circumferentially displaced relative to the vanes and/or omission of one or more flow modifying features, i.e., inclusion of fewer flow-modifying features than cooling vanes. Similarly, more than one circumferential row of in-line or staggered flow-modifying features may be included in a particular application where the additional row(s) help further focus the cooling air flow into the radially outer cooling channels.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.